When distributing powdered material through a hopper the generation of “rat holes” is a well known effect. Starting from the assumption that a bulk of powdered material has a flow direction through the hopper, which generally is the case, rat holes may be defined as cavities formed when an upstream portion of the bulk does not follow the movement of a downstream portion of the bulk. The likelihood of these cavities being formed will be affected by properties of the powdered material, properties of the hopper, as well as processing properties, such as mean velocity of the bulk.
Such cavities may result in various drawbacks. One example is that unless the cavity collapses the flow of powdered material will stop into downstream processes, which is readily understood as being a drawback. Furthermore, as a cavity collapses a pressure wave may be generated and disturb dosing equipment arranged further downstream. Also, the formed cavity may entrain air into the bulk, which may affect a resulting downstream product, for example if the powder is subsequently mixed into a liquid to form a food product.
Thus, there is a desire in eliminating rat holes even before they appear.
Though hopper was mentioned as an example in the above, the same problem may occur as when removing powder from a powder silo, a big-bag emptying station etc. and the applicability of the present invention is therefore not limited to hoppers only.
The problem as such is not new, rather several solutions have been presented over the years. To mention a few examples air may be injected into the powder bulk, and there may be an agitation of the bulk. The present invention aims at providing an improved arrangement for avoiding the occurrence of rat holes.